A fuel cell is a power generation device which converts chemical energy of a fuel into electrical energy by a electrochemical reaction within a fuel cell stack without combusting the fuel. The fuel cell may be used to supply power for an industry, a household, and vehicle driving and further to supply power to small electric/electronic products, in particular, portable devices.
Currently, as a power supply source for driving a vehicle, a polymer electrolyte membrane fuel cell (PEMFC) and a proton exchange membrane fuel cell (PEMFC) type which may have the greatest power density among the fuel cells have been developed. In particular, the polymer electrolyte membrane fuel cell and the proton exchange membrane fuel cell (PEMFC) may have a rapid starting time and a rapid power conversion reaction time due to their low operating temperature.
The polymer electrolyte membrane fuel cell typically include: a membrane electrode assembly (MEA) including catalytic electrode layers where the electrochemical reaction is generated and a solid polymer electrolyte membrane where protons passes and the catalytic electrode layers are attached; a gas diffusion layer (GDL) which serves to uniformly distribute reaction gases and transfer generated electrical energy; a gasket and a fastener which maintain air tightness and proper fastening pressure of the reaction gases and cooling water; and a bipolar plate where the reaction gases and the cooling water pass.
In an assembly of the fuel cell stack, a combination of the membrane electrode assembly and the gas diffusion layer is positioned at the innermost portion of the cell as major components. In the membrane electrode assembly, the catalytic electrode layers such as an anode and a cathode where a catalyst is disposed are provided for reaction sites of hydrogen and oxygen at both surfaces of the polymer electrolyte membrane, and an outer portion where the anode and the cathode are positioned is stacked with the gas diffusion layer, a gasket, and the like.
An outer portion of the gas diffusion layer is supplied with reaction gas such as hydrogen as fuel and oxygen or air as oxidizer and the outer portion of the gas diffusion layer is provided with a bipolar plate formed with a flow field where cooling water or air may pass.
A plurality of unit cells are stacked with unit cells, and then the outermost portion thereof is coupled with a current collector, an insulating plate, and an end plate for supporting the stacked cells, and the unit cells between the end plates are repeatedly stacked and fastened, thereby forming the fuel cell stack.
To obtain necessary potential in an actual vehicle, the number of the unit cells may vary based on potential required and stacking the unit cells may form a stack. Since potential generated from one unit cell is about 1.3 V, a plurality of cells are stacked in series to produce power required to drive a vehicle.
Meanwhile, in the fuel cell vehicle, an output voltage of the stack may be used to diagnose a state of the fuel cell.
The typical apparatus of diagnosing a state of a fuel cell stack in the related arts applies a sine wave (AC) of a multi frequency to the fuel cell stack and then measures a voltage of the fuel cell stack, detects a harmonic component by performing frequency conversion on the measured voltage, and then diagnoses the state of the fuel cell stack based on a magnitude of the harmonic component.
The typical state diagnostic apparatus of a fuel cell stack essentially includes a DC-DC converter which boosts a DC voltage and an inverter which converts the boosted DC voltage into an AC voltage such that a DC of the fuel cell stack may be overlapped with the AC current. However, the detection and diagnosis may be complicated configuration and thus expensive.